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decreasing pulse circuit

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Magnethicc

Member level 2
Hi Everyone,
I want to build a circuit which produces shorter and shorter square-wave pulses.
The frequency of the pulse is 62.5kHz and the pulse duration starts from ~100% duty down to ~200ns.
To help with the matter I have a circuit that generates 62.5kHz pulse (25% duty).

Does anyone have any idea on how to realize the circuit?
Thank you.

What controls the duration?
Do you want it to go from 100% to 0% in a fixed time period?
What frequency accuracy do you need for the 62.5kHz?

You can design it similar to an analog pwm generator. Triangle or sawtooth carrier generator, ramp generator for the modulation signal, comparator. You should also specify the modulation waveform, linear pulse width variation? Ramp time? Stopping at 200 ns PW?

@crustchow -
1. The duration of what?
2. yes
3. rather accurate. do note that I already have a 62.5kHz signal.

@FvM -
modulation waveform - linear or close to.
yes stopping at 200ns, dunno what pw is.
The idea seems good, any reason to not go that way in a soft-start kind of circuit? I want to produce the shorter and shorter sync pulses (when sync high than the converter does not switch).

Thank you

First of all, the accuracy of the 62.5 KHz has no bearing on the accuracy of the pulse width. “rather” is not a measure of accuracy. How do you covert “rather” to microseconds?

Aside from FVM’s analog suggestion, you could also use a small, cheap microcontroller.

If you want 200 nS resolution then a clocked method, like PWM, would have
to have 32 x 62.5 Kz = 2 Mhz clock. Do you want the solution derived from your
clock or can it be a seperate clock domain ?

This would be a couple of % accurate, with a xtal < .1% error. 1 chip.

Regards, Dana.

Hi,

how do 200ns resolution relate to 2MHz?

Klaus

My error, setup should be 10 Mhz clk :

Regards, Dana.

you could likely do it with 2 x 555 timer IC's, ( or the 556 equivalent ..)

Another possibility -

Regards, Dana.

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